MOD = 998244353
n = int(input())
a = list(map(int, input().split()))
numerator = 0
denominator = pow(2, n - 1, MOD)
dp = [{0: 0, -1: 0, 1: 0, 2: 0, -2: 0} for i in range(n + 1)]
for i, v in enumerate(a):
    if v == 1:
        dp[i + 1][1] = (pow(2, max(i - 1,0), MOD) + dp[i][1]) % MOD
        dp[i + 1][2] = dp[i][2]
        dp[i + 1][-1] = dp[i][-1]
        dp[i + 1][-2] = dp[i][-2]
        continue
    elif v == 2:
        dp[i + 1][2] = (dp[i][1] + pow(2, max(i - 1, 0), MOD)) % MOD
        dp[i + 1][-2] = dp[i][-1]
        continue
    elif v == -1:
        dp[i + 1][1] = dp[i][-1]
        dp[i + 1][-1] = (pow(2, max(i - 1,0), MOD) + dp[i][1]) % MOD
        dp[i + 1][2] = dp[i][-2]
        dp[i + 1][-2] = dp[i][2]
        continue
    elif v == -2:
        dp[i + 1][2] = dp[i][-1]
        dp[i + 1][-2] = (dp[i][1] + pow(2, max(i - 1, 0), MOD)) % MOD
        continue
    else:
        dp[i + 1][0] = 1

for i in range(n + 1):
    if i != n:
        numerator += dp[i][-2] * pow(2, n - i - 1, MOD)
    else:
        numerator += dp[i][-2]
    numerator %= MOD

#print(numerator, denominator)
ans = (numerator * pow(denominator, MOD - 2, MOD)) % MOD
print(ans)